Depron Wing

[Simon Chaddock]

Inspired by Glenn Moore's Depron Vulcan this is a build blog for a set of wings for the my WingDragon 4.

First I wanted to see is a simple Clark Y section on an otherwise identical wing made much difference to the performance & then I wanted to find out what 3mm Depron was like to build with.

My intention was to create a fully "built up" wing with the skin carrying all the stresses.

I made a master rib template that matched the chord & thickness of the original wing.

24 ribs gave an suitable pitch and although the ribs were cut out in one piece they were cut in two and glued to the spar. As it is only Depron it is not really a spar but acts as a shear web between the top and bottom skins.

The bottom skin glued to the RH wing. The extra webs between the inboard ribs are to provide support for the wing retaining bands. The short span ailerons are also built up with ribs and a top and bottom skin.

As the ailerons are a bit smaller I am using micro (5g) servos rather than the original 9g.

A close up of the servo mounting. The horn is set 45 degree forward to give differential movement to the top hinged aileron

I still have to add some servo extension leads before I glue on the top surface (sealing the servos in for ever!) and then finally add the leading edge.

So far I can say that for an old "balsa basher" Depron is easy enough to use, glues well and is a great deal cheaper.

[Chris Card]

Looks like some nice accurate workmanship there

Will the 5g servos be ok with such a large control surface?  The 5g servos I've used before seem quite a lot weaker than the 9g type.  Understandable I guess.

[Paul Adams]

Will be interested to see what happens when it complete. I have thought of building using a similar construction but am concerned about how much it will bend due to Depron being not very good in compression. I was considering putting a top and bottom spar at the deepest wing section to aid in this. Keep the posts going, I will watch with interest.

Its good to see someone experimenting and using a built up construction.

Regards Paul

[Chris Card]

Incidentally, I found this quick and easy version of a depron wing making method whilst surfing the web:

Easy Depron Wing

With score marks closer together the bend in the LE would be even smoother.  It's an interesting technique for making something relatively quickly, I might have to experiment some day - at least it will use up some of this depron I bought in a big pack from B&Q and haven't found a use for .

[Simon Chaddock]

A bit more progress

The underside of the wing with just the tip of the servo horn disturbing the otherwise bland surface.

With the servo leads extended & tested the top surface is glued on. It was tricky getting a glue bead on all structure before it set but the result is a nice smooth surface.

I have a bit of a thing about trailing edges. The theory says they should be infinitesimally thin. It required quite a bit of sanding of the inside of the skin trailing edges so that when they were glued together the result is less than the thickness of a penny!

Not tested yet but so far the wing feels as rigid as the solid foam original and is quite a bit lighter.

Next job - fix the top hinge aileron and servo push rod. I figure that as the ailerons are only half the size of the original & the Wing Dragon only weighs 25 ounces (700g) all up I believe (or rather hope) a 5g servo will be OK. Remember even at full chat the WD has to manage on just 50 watts/pound so I am following the late Colin Chapman principle - to improve performance, add lightness.

[Simon Chaddock]

I am afraid I went back to balsa for the leading edge simply because I had some suitable 3/8 stock which I sanded to shape. I am sure it could be done with 1mm sheet depron, so maybe next time.

The RH wing is now virtually complete so I can now bring the LH one up to the same standard.

Surprisingly the aileron hinge is just good quality sellotape, one strip between the vertical faces and another over the top. I tried this method out when I converted the original wing to top hinged ailerons. The result is very flexible yet remarkably rigid. We shall see how well it lasts.

With a 22 swg push rod there is absolutely no play in the linkage.

Obviously joining the two halves will add a bit of weight but so far it is on course to end up only 50% the weight of the original.

[Simon Chaddock]

The completed (but undecorated) wing on the Wing Dragon. Note no U/C, I just chuck it!

The wing does indeed weigh just half that of the original but then I have of course cheated a bit, the servos are lighter and it does not have the rather heavy plastic cover over the centre section.

The wing was joined by simply gluing the two halves together! I did make sure they matched up well. A simple test showed that a single layer of 1" sellotape over a butt joint was virtually as strong as the 3mm Depron itself so the wing joint has 3 overlapping layers top & bottom - light and cheap.

Even before the glue had set fully hard the wing would support 2 lbs at its centre (1.5 times the weight of the fuselage) when supported just at each tip. Such a test suggests it should be able to cope with an evenly distributed load equivalent to over 4g & probably quite a bit more. Not exactly super strong but then the WD is no pylon racer!

The old and new wings together. They are the same span, cord & thickness ratio.

We now have to see how it flies.

I think I could even use Depron for the 5cc's airframe!

[Brian Parker]

Depron+5cc=Heresy

[Chris Card]

Simon, the weight comparison isn't valid until you've finished it - ie. painted the depron red and transferred those tasteful decals

[Simon Chaddock]

Well I just couldn't wait with the weather so fine (and cold!) so I took it flying.

Actually it flew very well (no trim change required)l and quite a bit better than I expected from the relatively modest weight saving. The Clark Y seems to have a significantly better L/D as it was still climbing on half throttle. The roll rate was down a bit, to be expected with the smaller ailerons but there was no wing drop at the stall. The reduced drag also meant it could fly quite a bit faster so it would loop easily from level flight.

In fact it could fly a lot faster and this, coupled with a bit of finger trouble, resulted in the right wing parting company when pulling out of a dive. It appears to have failed in compression just beyond rib 2. The loose wing fluttered slowly down, the prop having cut through the servo lead. The ground impact of the one winged fuselage snapped off the fin (again) and the motor moved forward (again), but all easily fixed.

RH wing rebuild under way with a new inboard section and an extra support web between ribs 2 & 3 (where it failed). Note the chopped servo lead!

Depron and the 5cc? Well they used to make model aeroplanes out of bamboo and silk but I bet they would have used better materials if they had had access to them!

[Simon Chaddock]

All back together!

These pics show the area of the repair and the replaced leading edge. The joints in the skin are of course glued but will be taped over as well for strength.

To be honest I did not intend this to become a "repair blog" quite so soon - rather more gentle flying from now on!

[Paul Adams]

Sorry to hear it parted company. Just a thought you could add a strip of carbon (something like 5 x 0.5 mm) on top and bottom fitted at maximum wing thickness which would take the compression strain. Thinking about it, if you build another you could add these quite easy before you put the skin on.

[Glenn Moore]

Hi Simon,I normally use a 4mm carbon rod to reinforce the depron spar then a thin plywood dihedral keeper to reinforce the wing joint. I have a 46" and 68" spitfire and a 64" FW190 all using this set up and they take quite a bit of abuse with no problems so far.You can sometimes see the wings bend through the bottom of a loop which is quite interesting.

Glenn 

[Simon Chaddock]

Thanks Paul & Glenn for the advice.

To be fair it parted company because:-

1) it was flying much faster in a shallow dive than it ever did with the original wing

2) I panicked about the rate the ground was approaching and pulled up too hard, in fact it was actually going up when it failed, the fuselage went through a graceful arc into the ground.

and it will be flown again at the first opportunity.

Thus I am quite content that the new wing flew as well if not better than the original and I gained some useful experience in building (& repairing!) a relatively complex Depron structure.

And yes my next Depron wing will have a composite wing spar!
 

 

[Glenn Moore]

One of the things I like most about depron is its so easy to repair when you damage it

[David Phipps]

Hi Glen,

Silly question really, but what's the best glue to stick depron to depron ?

 Cheers.

[Simon Chaddock]

When I bought my Depron from Steve Webb Models "Foam to Foam" was recommended. It's pretty tacky but not instant which was good for the large areas. It does however set rock hard in a few hours.

Flew the repaired wing today. I made sure I did not break it and it works very well, so well in fact that getting down for an accurate landing took some doing.

[Glenn Moore]

I mostly use polyurethane adhesive as it gives you 5 - 10 minutes to get everything lined up and fixed in the right place and it is solid enough after an hour to work on. For smaller parts I use a hot glue gun as it speeds up construction.

Glad your repaired wing is flying again Simon.

[Simon Chaddock]

A bit more Depron

With its differential ailerons the rudder is virtually redundant, particularly as I hand launch with no U/C, so I have removed the rudder servo and push rod and fitted a Depron fixed fin & rudder (2x3mm sheets glued together).

The above combined with the weight already saved by the main wing and by moving the RX back a bit has allowed a big 2200mAh 3S LiPo to be installed for the same all up weight & CofG (the original 8 cell NiMH is only 1000mAh). That's equivalent to about 15 mins at full power (if the motor and ESC can stand it) or over 30 mins duration at cruise. Note the simple Velcro strap to stop it falling out!

The next step is to fit a V tail, made out of Depron of course. This is not just a sheet but a "built up" aerofoil structure similar to the wing. The V tail has the advantage that it is less likely to hit the grass on landing and no part of it is directly in the prop slipstream. It weighs no more than the original tail and the silk "cross over" hinges are much more flexible.

Next? Use the 4th channel for flaps, & big ones at that, but that will need another wing!

[Simon Chaddock]

The final development of my trusty Wing Dragon.

The V tail installed - using the original mounting plate and screws.

The home made double sided "clevis" with 12BA screws

The cockpit. It clips in so the battery (now a 1500mAh 3s) can't fall out and it improves the aerodynamics just a bit.

None of the basic structure has been changed in any way so it can be returned exactly to its original condition. For the record it now weighs 19 ounces (originally 23) and with 11.1 volts instead of 9.6 the thrust to weight is improved by nearly 25% and still with the humble brushed motor.

[Big Bandit]

Nice work Simon, it's good to see someone developing building techniques.

Cheers, Chris.

[Simon Chaddock]

As my Hamilcar X will use flaps I decided to add them to my Depron Wing Dragon to get a idea of what it would be like.

In its current state the WD only uses 3 of its 4 channels, the differential ailerons making the rudder rather unnecessary.

With the help of the radio forum I managed to modify the TX to add a switch isolate the rudder and transfer the function to a separate knob to work the flaps.

 

The WD with flaps fully down.

First trial today all OK but:

It was a bit windy and rather turbulent so a slow approach on full flap was not a sound strategy.

I made a design mistake when I mounted the flap servos close to the flaps as it moved the already rearward CofG back a bit further still. The result, rather marginal longitudinal stability, the last thing you want in turbulent conditions!

So whilst an impressively steep approach could be achieved it was not really under full control.

 

We live and learn. The CofG must go forward.

[Simon Chaddock]

Before just adding nose weight to move the CofG forward I thought I would first try reducing the longitudinal dihedral by packing up the trailing edge.

 

So I flew again today in calmer conditions. Much better, still a bit twitchy but it certainly flies impressively slowly on full flap, just over walking pace!I

It is so slow that the rather small ailerons have only just enough power to maintain adequate control. Its just as well the Hamilcar has big ailerons.

 

As a 2812 out runner is only half the weight of the 480 brushed motor a straight conversion should help move the CofG forward a bit and in addition the ESC is also bit heavier.

So here it is

Virtually no modification. The fuselage skin is simply clamped between the motor and a matching disc on the inside, with a small cut out for the wires.

A by-product of this installation is that the prop is further away from the wing which should make it quieter (the standard WD is remarkably noisy) and yes, with it over-hung so far from the mounting it has to be very carefully balanced. 

 

[Simon Chaddock]

Just to complete the story I was not happy with the prop overhung quite so far so I modified the prop driver a bit.

Flew quite a bit today and the 2812 outrunner does everything I expected.

The CofG is more or less back to where it was - it flies nicely.

It has quite a bit more thrust.

It is a lot quieter, in fact it is hard to hear when at any altitude.

and

On full flap it flies ridiculously slowly!

[Simon Chaddock]

As reported in "Field Tales" I smashed up my flapped Wing Dragon wing by flying it into a tree at high speed!

By no means a clean break as the branch crushed the wing from the LE back to the spar and the pusher prop completely chewed up the right hand flap. I was going to scrap it but then I hate to be beaten.

So - cut out the damaged bit

And stick it all back together!

Yes, the left and right bits are different lengths but it doesn't really matter as its just a plank wing. The old flaps are trimmed & simply glued back on. Two 5 inch tip sections to be added (already under construction), with new longer ailerons, and its back to its original span.

Its amazing what you can do with Depron!